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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Bart.VanAssche@wdc.com, dvyukov@google.com
Cc: linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	jthumshirn@suse.de, alan.christopher.jenkins@gmail.com,
	syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com,
	martin.petersen@oracle.com, axboe@kernel.dk,
	dan.j.williams@intel.com, hch@lst.de, oleksandr@natalenko.name,
	ming.lei@redhat.com, martin@lichtvoll.de, hare@suse.com,
	syzkaller-bugs@googlegroups.com, ross.zwisler@linux.intel.com,
	keith.busch@intel.com, linux-ext4@vger.kernel.org
Subject: Re: INFO: task hung in blk_queue_enter
Date: Tue, 22 May 2018 06:52:21 +0900	[thread overview]
Message-ID: <201805220652.BFH82351.SMQFFOJOtFOVLH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com>

Bart Van Assche wrote:
> On Wed, 2018-05-16 at 17:16 +0200, Dmitry Vyukov wrote:
> > On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche@wdc.com> wrote:
> > > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote:
> > > > diff --git a/block/blk-core.c b/block/blk-core.c
> > > > index 85909b4..59e2496 100644
> > > > --- a/block/blk-core.c
> > > > +++ b/block/blk-core.c
> > > > @@ -951,10 +951,10 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
> > > >               smp_rmb();
> > > > 
> > > >               wait_event(q->mq_freeze_wq,
> > > > -                        (atomic_read(&q->mq_freeze_depth) == 0 &&
> > > > -                         (preempt || !blk_queue_preempt_only(q))) ||
> > > > +                        atomic_read(&q->mq_freeze_depth) ||
> > > > +                        (preempt || !blk_queue_preempt_only(q)) ||
> > > >                          blk_queue_dying(q));
> > > > -             if (blk_queue_dying(q))
> > > > +             if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q))
> > > >                       return -ENODEV;
> > > >       }
> > > >  }
> > > 
> > > That change looks wrong to me.
> > 
> > Hi Bart,
> > 
> > Why does it look wrong to you?
> 
> Because that change conflicts with the purpose of queue freezing and also because
> that change would inject I/O errors in code paths that shouldn't inject I/O errors.

But waiting there until atomic_read(&q->mq_freeze_depth) becomes 0 is causing deadlock.
wait_event() never returns is a bug. I think we should not wait for q->mq_freeze_depth.

  reply	other threads:[~2018-05-21 21:53 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-28 11:24 syzbot
2018-05-15 11:45 ` Tetsuo Handa
2018-05-16 13:05   ` Tetsuo Handa
2018-05-16 14:56     ` Bart Van Assche
2018-05-16 15:16       ` Dmitry Vyukov
2018-05-16 15:37         ` Bart Van Assche
2018-05-21 21:52           ` Tetsuo Handa [this message]
2018-05-22 11:20             ` Tetsuo Handa
2018-06-01 10:10               ` Tetsuo Handa
2018-06-01 17:52                 ` Jens Axboe
2018-06-01 23:49                   ` Ming Lei
2018-06-02  0:49                     ` Jens Axboe
2018-06-02  0:56                       ` Jens Axboe
2018-06-02  2:36                       ` Ming Lei
2018-06-02  4:31                         ` Jens Axboe
2018-06-02  4:54                           ` Ming Lei
2018-06-02  8:07                             ` Martin Steigerwald
2018-06-02 13:48                             ` Jens Axboe
2018-06-05  0:27                   ` Tetsuo Handa
2018-06-05  0:41                     ` Ming Lei
2018-06-07  3:29                       ` Ming Lei
2018-06-07 13:19                         ` Tetsuo Handa
2018-06-04 11:46                 ` Dmitry Vyukov
2018-06-04 13:13                   ` Tetsuo Handa
2018-05-16 17:33     ` Alan Jenkins

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